Prefix with structure (5)
I believe the answer is:
infra
'prefix with structure' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for infra that I've seen before include "appearing later in book?" , "Dig is demeaning" , "lower down" , "-- Dig means degrading" , "Beneath (esp. 15)" .)